Oseltamivir phosphate [compound name: (−)-ethyl (3R,4R,5S)-4-acetamido-5-amino-3-(1-ethylpropoxy)-cyclohex-1-ene-1-carboxylate monophosphate] has a potent inhibitory activity against neuraminidase of influenza virus (Patent Document 1), and has been used as an active ingredient of Tamiflu (Registered Trade Mark) that is a preventive or therapeutic agent of influenza.
Oseltamivir phosphate has been used widely as a capsule formulation, and recently, formulated as dry syrup especially for convenience of pediatric use. In general, powder or granules including divided fine granules (hereinafter referred to as “granules and the like”) has to be stored under predetermined conditions once opened until used up. Compared to tablets and capsules that are packaged in unit dosage form, granules and the like are desired to have higher stability against light, humidity, temperature and the like in the storage environment. In particular, it is desired to provide granules and the like in which coloring, coagulation and aggregation are prevented. However, there has been no report on the preservation stability of the oseltamivir phosphate formulation of granules and the like. Also, there has been no report on the influence of additives on oseltamivir phosphate.    Patent Document 1: International Publication WO1998/007685 pamphlet